Ion microanalyzer

ABSTRACT

An ion microanalyzer wherein the intensity of a condenser lens for focusing an ion beam is periodically varied, to vary the spot diameter of the ion beam which is to impinge on a specimen, whereby the precision of analysis in the direction of the depth of the specimen can be enhanced.

United States Patent 11 1 1111 3,840,743 Tamura et al. [4 Oct. 8, 1974 1ION MICROANALYZER 3,535,516 10/1970 Munakata 250/310 3,628,012 12/1971Plows et a1 250/310 175] Inventors 2:32; fig a 33 g 3,702,398 11/1972Van Essen et al. 250/310 m a o apa I FOREIGN PATENTS OR APPLICATIONS[73] Asslgnee m Tokyo Japan 1,183,310 3/1970 Great Britain 250/309 1 1pp 327,683 New Developments in the Ion Microprobe Mass Analyzer, Lieblet a1. Hasler Research Center, 1968 30 Fori A I t' P' t Dt 1 J n 28 253ca Ion "on y a a 47 9866 Primary Examiner-Archie R. Borchelt a apanAssistant Examiner B' C. Anderson 52 us. (:1 250/307, 250/396, 250/309Attorney Firm-Crag Antonen [51] Int. Cl. H01j 37/26 58 Field of Search250/309, 310, 311, 307, 1 W

' 5 3 An 101'] microanalyzer wherein the intensity of a con- 2 96 denserlens for focusing an ion beam is periodically 5 References Cited varied,to yary the spot diameter of the ion beam UNITED STATES PATENTS WhlCh 1sto lmpmge on a specimen, whereby the precl- 2 422 807 6/1947 Smith250,310 sion of analysis in the direction of the depth of the 3:221:13311/1965 14311311011211.2131 :1, 250/311 Speclmen can be enhanced3,256,432 6/l966 Watanabe et a1 250/311 30' Claims, 8 Drawing Figures 24V t M ERECODER 2'3 PULSIVE SIGNAL SOURCE PATEMEU 81W 3.840.743

sum 1 or 3 Pmmwm 8w 3,840,743 NEH 20$ 3 FIG. 3b

FIG. 4

PULSIVE 1 SIGNAL SOURCE RECODER AMPLIFIER BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to improvements inan ion microanalyzer for the mass analysis of secondary ions which arecreated by irradiating a specimen with an ion beam.

2. Description of the Prior Art As compared with the other like devices,an ion microanalyzer has such features of being (a) capable of analysisof the thin surface layer of a specimen and (b) capable of measurementof a concentration distribution in the direction of the depth of aspecimen. Among such features, (b) is an especially important one, and

provides the following fields of uses:

Analysis of 1) iron and steel materials, (2) semiconductor materials,(3) surface treating materials, (4) insulator materials, (5) surfacepollution, (6) organic materials, and so forth.

The feature (b) is a merit not possessed by prior art analysis means,and is profitably put into practical use at present. As problems,however, the following points are mentioned:

i. Measurement of a concentration distribution in the direction of thedepth of a specimen in a range from'a surface portion of the specimen toa comparatively deep layer, as for example several p. to severalhundreds u.

ii. The case where, regarding the measurement of a concentrationdistribution in the direction of the depth FIG. 5 is a diagram showingmeasured results of the concentration distribution of boron (B) within aspecimen of silicon (Si) as taken in the direction of the depth of thespecimen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS which, as shown in FIG. la, thedensity is high at the central part and low at the peripheral part. Whenthe 1 ion beam having such distribution is radiated on the of aspecimen, a precision especially being smaller than several tens A isrequested.

The problems (i) and (ii) are important for future studies on thesurface or the thin surface layer of a specimen. If they are solved bythe analyzing procedure of the ion microanalyzer, the ion microanalyzerwill play an important role in the above-mentioned fields conjointlywith its high sensitivity.

SUMMARY OF THE INVENTION An object of the present invention is toprovide an ion microanalyzer which has a remarkably enhanced precisionof analysis in the direction of the depth of a specimen.

In order to accomplish this object, the present invention is constructedsuch that the intensity of at least one electron lens for focusing anion beam is varied, thereby to vary the spot diameter of the ion beam bywhich a specimen is irradiated.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la and lb are diagrams forexplaining the relation between the density distribution of a primaryion beam and the etching profile of a specimen irradiated by the ionbeam;

FIGS. 2a and 2b are diagrams illustratingthe principle of the presentinvention;

FIG. 3a is a schematic view for explaining a method of forming ion beamsas in FIG. 20, while FIG. 3b is a diagram showing voltages V, and Vwhich are applied to a condenser lens in order to obtain the ion beamshaving intensities and beam diameters as in FIG. 2a;

FIG. 4 is a schematic view showing an embodiment of the presentinvention; and

specimen, the specimen comes to have an etching profile which, as shownin FIG. lb, corresponds to the beam densities. When, under such state,secondary ions emitted from the specimenare analyzed by a mass analyzingdevice, the secondary ions ejected from parts of different depths as apoint C at the central portion and parts d and d at the peripheralportions shown in FIG. 1b are simultaneously detected. As a result, themeasuring precision of a concentration distribution in the direction ofthe depth, namely, the resolution in the direction of the depth isinferior. Even when the specimen is irradiated by a comparativelyuniform ion beam the precision is not high on account of influences ofthe peripheral part of the beam. The problem is serious in the analysesof a thin film and a thin layer in the surface portion of a specimen.

The present'invention has been developed to eliminate the disadvantageof the prior art as stated above, and the principle of the invention isas'will be described hereunder. The spot diameter of an ion beam isvaried on a specimen with time. First, the surface of the specimen isirradiated by the ion'beam of large current and large spot, to carry oution etching of wide area. Subsequently, the beam is made fine,the'central part of the etched area isirradiated by the fined beam, andsecondary ions emitted from the irradiated part are analyzed. Theseoperationsare repeated, whereby the concentration distribution in thedirection of the depth can be measured with high precision. FIGS. 2a and2b illustrate these results.

Reference numerals l and 2 in FIG. 2a designate the intensitydistributions of beams in the case where the intensity of anelectrostatic lens 5 (FIG. 3a) is changed as shown in FIG. 3b,respectively. FIG. 3a shows a lens system which focuses an ion beam,emitted from an ion source 3, on a specimen 8 by means of the condenserlens 5 and an objective lens 7. FIG. 3b shows lens voltages to beapplied to the condenser lens 5. When the voltages V, and v having thesquare waveform are applied to the condenser lens 5, the ion beam isfocused as illustrated by solid lines and broken lines in FIG. 3a

in correspondence with the respective applied voltages. With the ionbeams thus focused, the specimen is etched. In this case, the intensitydistributions of the beams on the specimen correspond to the curves 1and 2 shown in FIG. 2a. When the voltages in the form of the squarewaves are applied to the condenser lens, the

, etching profile as illustrated in FIG. 2b is formed in the ing thetime ratio of t /t of the square wave voltages illustrated in FIG. 3b.

In this manner, the analyzed outputs of secondary ions ejected from theetching profiles of the specimen in correspondence with the voltages Vand V are pro vided from the mass analyzing device. If, in this case,the outputs of the mass analyzing device are taken out in synchronismwith the intensity changes of the condenser lens or with the square wavevoltages, then only the outputs in the cases of the lens voltage V or Vcan be derived. It is accordingly made possible to analyze only theparts of l, l" and 2', 2" in FIG. 212. Thus, according to the presentinvention, the precision of analysis in the direction of the depth canbe arbitrarily selected by varying the ratio t /t in FIG. 3b.

Description will now be made of an embodiment of the present invention,reference being had to FIG. 4. First, the whole construction of theapparatus will be explained. When broadly classified in function, theapparatus is composed of a primary ion-radiating system and a massanalyzing device of the double focusing type. The primary ion-emittingsystem consists mainly of an ion gun 26, a condenser lens 5, a diaphragmor aperture 6, an objective lens 7, a deflecting electrode 9 and ashield electrode 25. An ion beam emitted from the ion gun 26 is focusedon a specimen 8 by a condenser lens 5 and the objective lens 7. Thefocused state is adjusted by changing the electric potential of anintermediate electrode 5 or 7 of the electrostatic lens 5 or 7.Especially, the intensity of the beam is changed by the condenser lens5. The determination of a place on the specimen to be analyzed, is doneeither by moving the specimen or by moving the beam with the deflectingelectrode 9.

The spot diameter of the ion beam on the specimen can be varied to anydesired value of from I u to several hundreds p. by the combinationbetween the condenser lens and the objective lens.

The mass analyzing device consists of a secondary ion-drawing outelectrode 10, an electrostatic lens 11 for correcting the trajectory ofa secondary ion beam, a slit 13, an electric field device 14, a slit 15,a magnetic field device 16 having an exciting coil (not shown), a slit17, a slit 19, an electron multiplier 20, an amplifier 22, a recorder 23and a switch 24,.and deflecting electrodes 12 and 18 which are attachedanew for the purpose of performing the present invention.

Secondary ions emitted from the specimen are subjected to energyselection by the electric field device 14. Then, they are introducedinto the magnetic field device 16, and are analyzed therein. Theanalyzed output is detected by the electron multiplier 20. Thereafter,the detected signal is amplified by the amplifier 22, and is recorded bythe recorder 23.

A power source 3] is composed of a power source section for supplying alens voltage 8,, and a power source section for supplying a square wavevoltage S which is synchronized with the lens voltage or is a functionof the same.

In the performance of the present invention, the following methods havebeen adopted:

1. The intensity of the primary ions and the diameter of the beam spotare varied in the form of step waves. In synchronism with the stepwaves, the potential of the deflecting electrode 12 disposed between thespecimen 8 and the electric field device 14 is varied in the form ofsquare waves. Thus, the secondary ions are detected at specified timesand at specified time intervals. More concretely, the square wavevoltage S having V and V as its amplitudes is applied to the condenserlens 5. The deflecting electrode 12 or 18 is applied with the squarewave voltage S of an amplitude V in synchronism with the voltage S, onlyfor a period of time from t to t to turn on and off the input or outputof the mass analyzing device. That is, only when the voltage V, isapplied as the lens voltage (t t t t the secondary ions are introducedinto the mass analyzing device, or the analyzed output is derivedtherefrom. During the periods t t t t during which the voltage V isapplied, the secondary ions are not introduced, or the analyzed outputis not derived.

2. Similarly to the method (I the stepped voltage S, is applied to thecondenser lens 5. The signal S is applied to the specimen 8 and theshield electrode 25. Thus, the analyzed output is provided from the massanalyzing device only during the periods t t t t 3. As in the method(I), the sensitivity of the detection system may be turned on and off insynchronism with the signal 5,, the detection system consisting of theelectron multiplier 20, amplifier 22 and recorder 23. For example, theamplification degree of the amplifier 22 may be changed.

4. As in the method (I), the electric field 14 or the magnetic field 16are varied. In this case, ions of any mass are inhibited from passingthrough the slit 19.

In the foregoing embodiments, the mass analyzing device may have onlythe magnetic field device without the electric field device. Theelectrostatic lenses may be replaced with a single lens, and a magneticlens or lenses may also be employed. Further, the square wave voltage Smay also be applied to the objective lens 7, or to both the condenserlens 5 and the objective lens 7. The square wave voltage S need not bealways varied periodically, but it is only required to be changed withtime.

An example of results obtained by the above methods (1) to (4) isillustrated in FIG. 5. The specimen used as shown at Si is a siliconwafer epitaxially grown, and has a distribution of two orders ofconcentrations of boron (B) in a surface layer of 0.5 ,lL. In thefigure, a curve (i) represents the concentration distribution of B astheoretically evaluated. A curve (ii) shows the measured resultsobtained by the prior art method. A curve (iii) shows the measuredresults in the case of applying the present invention. As apparent fromthe figure, the data obtained by the prior art method are considerablydifferent from the theoretical values, to considerably expand theconcentration distribution in the direction of the depth. This meansthat the ion current density distribution of the primary ion beam is notuniform, resulting in an inferior resolution along the depth. Incontrast, in the case of (iii) with the present invention applied, thedata conform to the theoretical values well, and represent theconcentration distribution of B along the depth precisely.

As for the method of taking out the outputs of the mass analyzing devicein synchronism with the intensity variation of the condenser lens, itmay also be made to establish electric and magnetic fields in thepassage of the secondary ion beam anew and to change the intensitiesthereof.

What is claimed is:

1. In an ion microanalyzer comprising ion beam generating meansincluding an ion source device for emitting an ion beam; at least oneion lens disposed along the path of said ion beam for focusing said ionbeam on a specimen, first deflecting means for deflectingsaid ion beam;mass analyzing means for analyzing secondary ions emitted from saidspecimen by ion impingement; and detecting means for detecting theoutput of said mass analyzing device, the improvement which comprisesfirst control means for periodically varying the focus of said ion lens,said first control means including first signal source means forsupplying a first periodic signal to said ion lens, and second controlmeans for periodically inhibiting the output of said detecting means insynchronism with the intensity variation of said ion lens.

2. An ion microanalyzer according to claim 1, wherein said secondcontrol means includes means for periodically varying the analyzingoperation of said mass analyzing device in synchronism with theintensityvariation of the ion lens.

3. An ion microanalyzer according to claim 1, wherein said secondcontrol means'includes means for varying the output of said massanalyzing device in synchronism with the intensity variation of the ionlens.

4. An ion microanalyzer according to claim 1, wherein said secondcontrol means includes means for varying the sensitivity of saiddetecting device in synchronism with the intensity variation of the ionlens.

5. An ion microanalyzer according to claim 1 wherein said ion lensincludes three electrodes disposed in parallel with one another, theintermediate one of said electrodes being connected to said first control means.

6. An ion microanalyzer according to claim 1 wherein said second controlmeans comprises second deflecting means disposed between said specimenand said mass analyzing device for deflecting said secondary ions andsecond signal source means for supplying a second periodic signal tosaid second deflecting means in synchronism with the first periodicsignal.

7. An ion microanalyzer according to claim 2 wherein said mass analyzingdevice includes an electric field device and a magnetic field device,and said second control means comprises second signal source means forsupplying a second periodic signal to said electric field device insynchronism with the first periodic signal.

8. An ion microanalyzer according to claim 2 wherein said mass analyzingdevice includes an electric field device and a magnetic field device,and said second control means comprises second signal source means forsupplying a second periodic signal to said magnetic field in synchronismwith the first periodic signal.

9. An ion microanalyzer according to claim 3 wherein said second controlmeans includes third deflecting means and second signal source means forsupplying a second periodic signal to said third deflecting means insynchronism with the first periodic signal.

' l0. Method of measurement of the concentration distribution in thedirection of the depth of a specimen, comprising the steps of generatingan ion beam, focusing said ion beam on a portion of a specimen, massanalyzing the secondary ions generated by impingement of said ion beamon said specimen, detecting the mass analyzed secondary ions insynchronism with variation of the focusing of said ion beam to vary thediameter of the ion beam impinging on said specimen so as to vary thepenetration pattern of said ion beam in said specimen.

11. Method as defined in claim 10 wherein .said focusing is variedperiodically between first and second values and said detecting isperformed in synchronism with one of said first and second values offocusing.

12. Method as defined in claim 10 wherein said focusing is variedperiodically between first and second values and said mass analyzing isperformed in synchronism with one of said first and second values offocusmg.

13. Method as defined in claim 10 wherein said focusing is variedperiodically between first and second values and the sensitivity of saiddetecting is varied in synchronism with one of said first and secondvalues of focusing.

14. Method as defined in claim 10 wherein said focusing is variedperiodically between first and second values and the generation ofsecondary ions at said specimen is inhibited in synchronism with one ofsaid first and second, values of focusing.

15. An ion microanalyzer comprising:

means for emitting a primary ion beam;

means for irradiating a specimen with said primary ion beam, said meansincluding at least one electrostatic lens disposed along the path ofsaid ionbeam;

means for varying alternately the spot diameter of the ion beam which isirradiated on a specimen by varying alternately a potential applied tosaid electrostatic lens; i

means for deflecting said ion beam;

means for analyzing secondary ions emitted from said specimen, saidmeans consisting of a mass analyzer;

means for detecting and recording the output of said means for analyzingsecondary ions in synchronism with said varying means; whereby aprecision analysis of the concentration distribution in the directiontoward the depth of said specimen can be enhanced. 16. Anionmicroanalyzer according to claim 15, in which said means for varyingalternately the spot diameter of the ion beam comprises means forvarying periodically the spot diameter of the ion beam.

17. An ion microanalyzer according to claim 15, which further comprisesmeans for shielding the specimen and means for controlling the abilityof said secondary ions emitted from said specimen to enter said meansfor analyzing secondary ions in synchronism with said means for varyingalternately the spot diameter of the ion beam.

18. An ion microanalyzer according to claim 16, which further comprisesmeans for controlling the output of secondary ions of said means foranalyzing sec-' ondary ions, and said means for detecting and recordingthe output of said means for analyzing secondary ions.

19. An ion microanalyzer according to claim 18, in which said means forcontrolling the output of secondary ions comprises means for controllingthe transmission of said secondary ions through said mass analyzer insynchronism with said means for varying alternately the spot diameter ofthe ion beam.

20. An ion microanalyzer according to claim 19, in which said massanalyzer comprises at least one of an electric field device and amagnetic field device.

21. An ion microanalyzer according to claim 20, in which said means forcontrolling the output of secondary ions comprises a deflectingelectrode provided between said sample and said mass analyzer.

22. An ion microanalyzer according to claim 20, in which said means forcontrolling the output of secondary ions is a deflecting electrodeprovided between said mass analyzer and said means for detecting theoutput of said means for analyzing secondary ions.

23. An ion microanalyzer according to claim 20, in which said means forcontrolling the output of secondary ions comprises means for controllingthe intensity of said electric field device.

24. An ion microanalyzer according to claim 20, in which said means forcontrolling the output of secondary ions comprises means for controllingthe intensity of said magnetic field device.

25. An ion microanalyzer according to claim 15, in which said means forcontrolling the output of secondary ions comprises means for controllingthe sensitivity of said means for detecting and recording the output ofsaid means for analyzing secondary ions.

26. An ion microanalyzer according to claim 25, in which said means fordetecting the output of said means for analyzing secondary ionscomprises a photomultiplier, and said means for controlling the outputof secondary ions comprises means for controlling the sensitivity tosecondary ions of said photomultiplier.

27. An ion microanalyzer according to claim 25, in

which said means for detecting the output of said means for analyzingsecondary ions comprises a photomultiplier and an amplifier connected tosaid photomultiplier, and said means for controlling the output ofsecondary ions comprises means for controlling the amplification factorof said amplifier.

28. An ion microanalyzer according to claim 15, in which saidelectrostatic lens consists of a group of three electrodes disposed inparallel with one another, and said means for varying alternately thespot diameter of the ion beam is connected to an intermediate electrodeof said three electrode group.

29. Method of measurement of the concentration distribution in thedirection of the depth of a specimen, comprising the steps of emitting aprimary ion beam;

irradiating on a specimen with said ion beam having large spot diameterto etch said specimen;

irradiating a specimen with said ion beam having a small spot diameter;

mass analyzing secondary ions emitted with irradiation of said primaryion beam;

repeating the irradiation of said specimen with said ion beam havinglarge and small spot diameters; detecting and recording an output ofsaid secondary ions being mass analyzed; and controlling the output ofsecondary ions in synchronism with irradiation of said specimen withsaid primary ion beam having large and small diameters. 30. Method asdefined in claim 29, in which said irradiation of the specimen isrepeated periodically.

1. In an ion microanalyzer comprising ion beam generating meansincluding an ion source device for emitting an ion beam; at least oneion lens disposed along the path of said ion beam for focusing said ionbeam on a specimen, first deflecting means for deflecting said ion beam;mass analyzing means for analyzing secondary ions emitted from saidspecimen by ion impingement; and detecting means for detecting theoutput of said mass analyzing device, the improvement which comprisesfirst control means for periodically varying the focus of said ion lens,said first control means including first signal source means forsupplying a first periodic signal to said ion lens, and second controlmeans for periodically inhibiting the output of said detecting means insynchronism with the intensity variation of said ion lens.
 2. An ionmicroanalyzer according to claim 1, wherein said second coNtrol meansincludes means for periodically varying the analyzing operation of saidmass analyzing device in synchronism with the intensity variation of theion lens.
 3. An ion microanalyzer according to claim 1, wherein saidsecond control means includes means for varying the output of said massanalyzing device in synchronism with the intensity variation of the ionlens.
 4. An ion microanalyzer according to claim 1, wherein said secondcontrol means includes means for varying the sensitivity of saiddetecting device in synchronism with the intensity variation of the ionlens.
 5. An ion microanalyzer according to claim 1 wherein said ion lensincludes three electrodes disposed in parallel with one another, theintermediate one of said electrodes being connected to said firstcontrol means.
 6. An ion microanalyzer according to claim 1 wherein saidsecond control means comprises second deflecting means disposed betweensaid specimen and said mass analyzing device for deflecting saidsecondary ions and second signal source means for supplying a secondperiodic signal to said second deflecting means in synchronism with thefirst periodic signal.
 7. An ion microanalyzer according to claim 2wherein said mass analyzing device includes an electric field device anda magnetic field device, and said second control means comprises secondsignal source means for supplying a second periodic signal to saidelectric field device in synchronism with the first periodic signal. 8.An ion microanalyzer according to claim 2 wherein said mass analyzingdevice includes an electric field device and a magnetic field device,and said second control means comprises second signal source means forsupplying a second periodic signal to said magnetic field in synchronismwith the first periodic signal.
 9. An ion microanalyzer according toclaim 3 wherein said second control means includes third deflectingmeans and second signal source means for supplying a second periodicsignal to said third deflecting means in synchronism with the firstperiodic signal.
 10. Method of measurement of the concentrationdistribution in the direction of the depth of a specimen, comprising thesteps of generating an ion beam, focusing said ion beam on a portion ofa specimen, mass analyzing the secondary ions generated by impingementof said ion beam on said specimen, detecting the mass analyzed secondaryions in synchronism with variation of the focusing of said ion beam tovary the diameter of the ion beam impinging on said specimen so as tovary the penetration pattern of said ion beam in said specimen. 11.Method as defined in claim 10 wherein said focusing is variedperiodically between first and second values and said detecting isperformed in synchronism with one of said first and second values offocusing.
 12. Method as defined in claim 10 wherein said focusing isvaried periodically between first and second values and said massanalyzing is performed in synchronism with one of said first and secondvalues of focusing.
 13. Method as defined in claim 10 wherein saidfocusing is varied periodically between first and second values and thesensitivity of said detecting is varied in synchronism with one of saidfirst and second values of focusing.
 14. Method as defined in claim 10wherein said focusing is varied periodically between first and secondvalues and the generation of secondary ions at said specimen isinhibited in synchronism with one of said first and second values offocusing.
 15. An ion microanalyzer comprising: means for emitting aprimary ion beam; means for irradiating a specimen with said primary ionbeam, said means including at least one electrostatic lens disposedalong the path of said ion beam; means for varying alternately the spotdiameter of the ion beam which is irradiated on a specimen by varyingalternately a potential applied to said electrostatic lens; means fordeflecting said ion beam; means for analyzing secoNdary ions emittedfrom said specimen, said means consisting of a mass analyzer; means fordetecting and recording the output of said means for analyzing secondaryions in synchronism with said varying means; whereby a precisionanalysis of the concentration distribution in the direction toward thedepth of said specimen can be enhanced.
 16. An ion microanalyzeraccording to claim 15, in which said means for varying alternately thespot diameter of the ion beam comprises means for varying periodicallythe spot diameter of the ion beam.
 17. An ion microanalyzer according toclaim 15, which further comprises means for shielding the specimen andmeans for controlling the ability of said secondary ions emitted fromsaid specimen to enter said means for analyzing secondary ions insynchronism with said means for varying alternately the spot diameter ofthe ion beam.
 18. An ion microanalyzer according to claim 16, whichfurther comprises means for controlling the output of secondary ions ofsaid means for analyzing secondary ions, and said means for detectingand recording the output of said means for analyzing secondary ions. 19.An ion microanalyzer according to claim 18, in which said means forcontrolling the output of secondary ions comprises means for controllingthe transmission of said secondary ions through said mass analyzer insynchronism with said means for varying alternately the spot diameter ofthe ion beam.
 20. An ion microanalyzer according to claim 19, in whichsaid mass analyzer comprises at least one of an electric field deviceand a magnetic field device.
 21. An ion microanalyzer according to claim20, in which said means for controlling the output of secondary ionscomprises a deflecting electrode provided between said sample and saidmass analyzer.
 22. An ion microanalyzer according to claim 20, in whichsaid means for controlling the output of secondary ions is a deflectingelectrode provided between said mass analyzer and said means fordetecting the output of said means for analyzing secondary ions.
 23. Anion microanalyzer according to claim 20, in which said means forcontrolling the output of secondary ions comprises means for controllingthe intensity of said electric field device.
 24. An ion microanalyzeraccording to claim 20, in which said means for controlling the output ofsecondary ions comprises means for controlling the intensity of saidmagnetic field device.
 25. An ion microanalyzer according to claim 15,in which said means for controlling the output of secondary ionscomprises means for controlling the sensitivity of said means fordetecting and recording the output of said means for analyzing secondaryions.
 26. An ion microanalyzer according to claim 25, in which saidmeans for detecting the output of said means for analyzing secondaryions comprises a photomultiplier, and said means for controlling theoutput of secondary ions comprises means for controlling the sensitivityto secondary ions of said photomultiplier.
 27. An ion microanalyzeraccording to claim 25, in which said means for detecting the output ofsaid means for analyzing secondary ions comprises a photomultiplier andan amplifier connected to said photomultiplier, and said means forcontrolling the output of secondary ions comprises means for controllingthe amplification factor of said amplifier.
 28. An ion microanalyzeraccording to claim 15, in which said electrostatic lens consists of agroup of three electrodes disposed in parallel with one another, andsaid means for varying alternately the spot diameter of the ion beam isconnected to an intermediate electrode of said three electrode group.29. Method of measurement of the concentration distribution in thedirection of the depth of a specimen, comprising the steps of emitting aprimary ion beam; irradiating on a specimen with said ion beam havinglarge spot diameter to etch said specimen; irradiating a specimen withsaid ion beam having a small spot Diameter; mass analyzing secondaryions emitted with irradiation of said primary ion beam; repeating theirradiation of said specimen with said ion beam having large and smallspot diameters; detecting and recording an output of said secondary ionsbeing mass analyzed; and controlling the output of secondary ions insynchronism with irradiation of said specimen with said primary ion beamhaving large and small diameters.
 30. Method as defined in claim 29, inwhich said irradiation of the specimen is repeated periodically.